The purpose of this research is to investigate the functional changes in subhuman primates that occur after selective ablaton of different portions of the equilibrium system. Bodily dysequilibrium and compensation and oculomotor dysfunction and recovery are measured quantitatively in these subjects. Bodily equilibrium function tests (the squirrel monkey rail test and platform runway tests - for dynamic bodily equilibrium, and the squirrel monkey stabilitimeter - for static bodily equilibrium) which are based upon behavioral conditioning procedures, permit quantitative and thus comparable observations along the post-ablation time course. Experimental categories include: selective partial ablation of brain stem structures, cerebellar flocculus, otolith end organs, etc. The effects of visual cue change and physical exercise upon equilibrium function, and compensation from ablative lesions, will also be studied. Morphological confirmation of the experimental lesion will be performed in all subjects upon the completion of functional examinations. This project will provide important information after selective ablation of individual parts of the equilibrium system and will contribute to the understanding of clinical vestibular dysfunction, and the recovery from loss of vestibular end organs.